What are Oklahoma's pier and anchor rules for manufactured homes?
In short: New manufactured homes in Oklahoma must be installed to the federal HUD installation standard or the manufacturer's approved instructions by a state-licensed installer. Previously occupied (used) homes follow Oklahoma's own rules: block footings, frame piers no more than 6 feet apart, limited shims, and diagonal anchor ties. These supports sit near the surface, where Oklahoma clay swells and shrinks the most.
Who sets the installation rules?
Manufactured home installation in Oklahoma falls under Title 765, Chapter 37 of the Oklahoma Administrative Code, administered by the Oklahoma Used Motor Vehicle, Dismantler, and Manufactured Housing Commission 1.
- New homes: installation, including site preparation, must follow HUD's Manufactured Home Model Installation Standards (24 CFR Part 3285) or the manufacturer's approved installation instructions 1.
- Licensed installers: using an installer not licensed by the Commission at the time of installation is an unacceptable procedure, and a dealer who hires one may face penalties 1.
- Frost line: for permanent installations, the installer determines the frost line from the manufacturer's instructions or the local building authority 1. See freeze-thaw and frost depth.
- Storage: a new home held more than 30 days by a retailer, installer or manufacturer must be temporarily supported per the manufacturer's instructions 1.
For how these homes are built and supported, see manufactured homes on piers.
What are the support rules for used homes (OAC 765:37-7-3)?
Footings
A footing is the pad that spreads a pier's load onto the soil.
| Item | Requirement |
|---|---|
| Footing options | Three 4x8x16 solid concrete blocks, or one solid 4x16x16 block 2 |
| Minimum footing area | 384 square inches 2 |
| Minimum tested capacity | 6,000 pounds load-bearing per footing 2 |
| Assumed soil bearing | At least 1,500 psf unless site conditions call for less 2 |
| Soil under footing | Organic material removed; firm undisturbed soil or fill compacted to at least 90% 2 |
If site conditions suggest a lower bearing value, the rule says to consult a professional engineer, registered architect or licensed geologist, and soil testing such as penetrometer readings can change the assumed value 2. Soil bearing and plasticity are explained in soil testing and lab values.
Piers
| Pier location and height | Allowed construction |
|---|---|
| Frame piers under 36 in | Single 8x8x16 blocks, or rated steel piers up to 36 in 2 |
| Frame piers 36 to 67 in, and corner piers over three blocks | Double interlocked blocks 2 |
| Mate-line, perimeter and opening piers up to 54 in | Single blocks 2 |
| Mate-line, perimeter and opening piers over 54 to 67 in | Double interlocked blocks 2 |
Spacing, clearance and shims
- Piers under each main frame beam: no more than 6 feet on center 2.
- Where an open span exceeds 10 feet, intermediate piers no more than 10 feet on center 2.
- End piers: centered no more than 2 feet from the frame ends 2.
- Clearance: at least 12 inches between the lowest frame member and the ground 2.
- Shims: nominal 4x6x1 shims used in pairs, driven tight, taking up no more than one inch of height 2.
What are the anchoring rules for used homes (OAC 765:37-7-4)?
Anchors and ties hold the home down and resist sideways movement in wind.
- Diagonal ties: spaced no more than 11 feet apart on a side; an individual spacing may exceed that by 10% as long as the average stays within 11 feet 3.
- End ties: the diagonal tie nearest each end must be within 2 feet of that end 3.
- Anchor strength: a minimum total load of 4,725 pounds and a working capacity of 3,150 pounds 3.
- Lateral stability: anchors are installed per the manufacturer, which may include stabilizer plates or poured concrete collars 10 inches across and 18 inches deep 3.
Why do surface piers move on Oklahoma clay?
The rules above place block footings on firm undisturbed soil or compacted fill after organic material is removed 2. Where that soil is expansive clay, it swells when wet and shrinks when dry. An Oklahoma State University study of soil suction across the state found that the depth affected by seasonal moisture change (the active zone) is roughly 0.5 to 4 meters, and that shallower soil is the most sensitive to climate 4. Because piers rest in that zone, the home can move as the soil does:
- Uneven heave and settlement: perimeter piers near drip lines and downspouts can rise or drop differently from interior frame piers. See heave vs settlement.
- Drainage: water pooling under a skirted home wets the clay under the footings. See surface drainage and grading.
- Shim limits: shims may take up no more than one inch of height 2, which limits how much releveling shims alone can do.
The shrink-swell and active zone guide explains why moisture changes are greatest near the surface.
Related
- Manufactured homes on piers
- Shrink-swell and active zone
- Surface drainage and grading
- Freeze-thaw and frost depth
- Codes and permits
Common questions
Who regulates manufactured home installation in Oklahoma?
The Oklahoma Used Motor Vehicle, Dismantler, and Manufactured Housing Commission licenses installers. Installing a home with an unlicensed installer is listed as an unacceptable procedure under Oklahoma Administrative Code 765:37.
How far apart can piers be under a used manufactured home in Oklahoma?
Piers under each main frame beam can be no more than 6 feet on center, and the end piers must be within 2 feet of the frame ends.
What soil strength does Oklahoma assume for manufactured home footings?
The rule assumes at least 1,500 pounds per square foot unless site conditions call for a lower value, in which case an engineer, architect or geologist should be consulted. Soil testing can change the assumed value.
How much shimming is allowed under a manufactured home?
Shims must be nominal 4x6x1 pieces used in pairs and driven tight, taking up no more than one inch of height.
How many anchor ties does a used manufactured home need?
Diagonal ties may be no more than 11 feet apart along each side, with the end ties within 2 feet of each end. Each anchor must resist 4,725 pounds total with a working capacity of 3,150 pounds.
Sources
- Okla. Admin. Code 765:37-7-1, Acceptable procedure Justia Regulations (Oklahoma Administrative Code)
- Okla. Admin. Code 765:37-7-3, Support Systems Cornell Law School Legal Information Institute
- Okla. Admin. Code 765:37-7-4, Anchoring for previously occupied manufactured homes Justia Regulations (Oklahoma Administrative Code)
- Soil matric suction and active zone depth in Oklahoma Oklahoma State University (SHAREOK repository)
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